Currently, wireless communication systems such as cellular phone systems and wireless local area networks (LANs) are widely used. In the field of wireless communication, discussions on the next generation of communication technologies are being continuously conducted to further improve the transmission speed and communication capacity. For example, in the 3rd Generation Partnership Project (3GPP), which is a standardization organization, a wireless communication system called Long Term Evolution-Advanced (LTE-A), which has been developed from Long Term Evolution (LTE), has been proposed.
There is a technique called a handover in the field of wireless communication as mentioned. A handover is, for example, a technique for switching a radio base station device (evolved UTRAN NodeB (eNB), hereinafter referred to as a “base station”) to which a mobile terminal device (mobile station, hereinafter referred to as a “terminal”) is communicably coupled. For example, when the intensity of radio waves received by a terminal becomes lower than a fixed value, the terminal changes its connection from the current base station to another by a handover, so that continuous wireless communication is achieved.
In this case, the base station determines whether a handover is to be performed and selects which base station is to be the target of a handover, for example, based on the radio quality detected by the terminal. For example, the terminal measures the intensities of radio waves of signals transmitted from a base station communicably coupled thereto and an adjacent base station located adjacent to the base station communicably coupled, and transmits their respective measurement results to the base station. The base station determines that the adjacent base station is to be the target of the handover when the intensity of radio waves of the adjacent base station is higher than that of the currently coupled base station and is higher than a threshold.
Unfortunately, a plurality of handovers may occur for a short time when the terminal is moving at high speed while performing data communication. Particularly, in urban areas in which the ranges covered by cells (cell ranges) are designed so as to overlap one another by using a plurality of base stations, there are many cases where such a situation occurs compared to other areas.
In these cases, for example, the base station serving as the source of a handover (the handover source) forwards data to a base station serving as the target of the handover (the handover target), and the target base station transmits the data to the terminal. However, since the terminal is moving at high speed, the terminal may be further handed over to another base station while the base station serving as the handover target is transmitting data, and thus the terminal may fail to receive the data. Accordingly, when a plurality of handovers occur for a short time, data loss and retransmission of the data lost are likely to occur.
Techniques concerning handovers are, for example, as follows. That is, in a control device in charge of a plurality of base stations, a frequency of handovers is stored for each permutation in which three base stations are sequentially arranged, the handover target is determined on the basis of that frequency, and the timing of the handover is predicted on the basis of ratio between communications times of the base stations.
Also, in a cell individual offset (CIO) setting control device, a CIO value that is used for correction of a radio quality result measured by a mobile station is corrected on the basis of a cell-stay period of user equipment (UE) that is included in communication history information, and thus the CIO value is set without performing a running test and the like.
Japanese Laid-open Patent Publication No. 2010-34789 and Japanese Laid-open Patent Publication No. 2010-187075 disclose related techniques.